1. Field of The Invention
The invention relates to a drop-and-add multiplexer for converting a frequency division multiplexed (FDM) signal with a large amount of channels and for receiving signals of additional channels.
2. Background Information
Digital frequency converters which generate frequency multiplex signals, particularly those of a large band width and high scanning frequency, by single channel conversion in interpolating digital frequency converters are known from German Published, Non-Examined Patent Applications 40 26 477 and 40 41 632, wherein a digital frequency multiplex conversion method with super scanning is described.
It is thus possible by conventional means to split a defined digital FDM signal into separate partial signals by means of decimating digital frequency converters, to regroup these signals or to replace some signals by others, and to combine them afterwards into a new FDM signal by means of interpolating digital frequency converters in a digital frequency converter (see FIG. 1).
Given the assumption that the same number of channels are occupied in the original FDM incoming signal and the modified FDM outgoing signal (I=J), FIG. 1 shows how incoming channel signal "i" is replaced by an outgoing new channel signal "j." In this case the decimating digital frequency converter DDFUi can be omitted.
The channel signals mutually contained in both FDM signals can be located, depending on the selection of the respective converter frequency, in different channel frequencies f.sub.iin .noteq.f.sub.out (f.sub.in, f.sub.out are the channel frequencies, i.e., the position of the channels in the FDA-spectrum).
It is also possible that I.noteq.J, in which case all decimating digital frequency converters (DDFU's) for channel signals to be eliminated can of course be omitted.